Poly(lactic acid)/poly(butylene-succinate-co-adipate) (PLA/PBSA) blend films containing thymol as alternative to synthetic preservatives for active packaging of bread

Antifungal films based on poly(lactic acid)/poly(butylene-succinate-co-adipate) (PLA/PBSA) blends containing 3 wt% (LT-PLA/PBSA) and 6 wt% (HT-PLA/PBSA) of thymol were prepared using blown film extrusion technique. In vitro antifungal activity of the films against Aspergillus spp. and Penicillium spp. was evaluated using a vapor contact assay. The antifungal films containing thymol were highly effective against fungal growth as compared to the neat PLA film and PLA/PBSA blend film. The addition of PBSA and thymol resulted in decreased glass transition temperature and melting temperature. All active films exhibited significantly lower tensile strength and Young's modulus but higher elongation at break compared to the neat PLA. The permeability coefficients of water vapor, oxygen, and carbon dioxide (CO2) of the PLA/PBSA blend films containing thymol were lower than those of the neat PLA film. The antifungal films were tested for bread packaging, compared with biaxially oriented polypropylene (BOPP) and neat PLA. Mold growth was observed on the bread packaged in LT-PLA/PBSA and HT-PLA/PBSA after storage for 7 and 9 d, respectively. Whereas, the bread in BOPP and neat PLA packaging showed visible mold growth after storage for 3 and 6 d, respectively. Yeast and mold counts increased throughout the storage period, which were 7.13, 5.83, 5.38 and < 1.00 log CFU g(-1) for BOPP, neat PLA, LT-PLA/PBSA, and HT-PLA/PBSA, respectively after storage for 9 d. In-package CO2 concentration was highly correlated with the yeast and mold counts. Highest CO2 was observed in BOPP, while lowest CO2 was observed in HT-PLA/PBSA followed by LT-PLA/PBSA.